The present invention relates to a vibration body for cutting, a vibration cutting unit and a processing apparatus which are used suitably for cutting operations of materials for forming a molding die for an optical element and others, as well as to a molding die made by using the processing apparatus, and to an optical element.
There is a technology to conduct cutting operations for materials including hard metal and glass which are cutting-resistant materials by vibrating a tip of a cutting tool such as a diamond tool, which is called vibration cutting. This technology is one to realize cutting operations causing less stress for both a cutting tool and a material to be cut, by the effects that a fine cut-in is carried out at high speed by vibration of a cutting edge, and chips generated in this case are bailed out by the vibrating cutting edge (for example, see Patent Documents 1, 2, 3 and 4). Owing to this vibration cutting operation, an amount of critical cut-in required for ordinary ductile mode cutting is improved to the level of several times, which makes it possible to conduct cutting operations for cutting-resistant materials at high efficiency.
In this vibration cutting operations, high speed vibration of 20 kHz or more is usually used for improving processing efficiency, because, if a frequency of vibration is enhanced, the aforesaid effects are also increased and cutting feed rate for the tool is enhanced in proportion substantially to the frequency. There is also an advantage that unpleasant noises are not generated from neither oscillator nor vibration body excited by the oscillator, because the aforesaid frequency of vibration exceeds a human audible zone.
As a method to generate the high speed vibration of this kind on a cutting edge of a cutting tool, steady vibration has been put to practical use as a standing wave by exciting a holding member that holds a tool with a piezoelectric element or with a super-magnetostrictor and by causing this holding member to resonate by bending vibration and axial vibration. In the method of this kind, the vibration body that supports a cutting tool is fixed with a flange-shaped supporting body provided on the outer periphery of the vibration body at a position of the vibration node or is clamped by screw-shaped supporting members at a position of the node portion of vibration to be fixed in a way that the vibration body is pressed by the pressure surrounding the vibration body.    (Patent Document 1) Unexamined Japanese Patent Application Publication No. 2000-52101    (Patent Document 2) Unexamined Japanese Patent Application Publication No. 2000-218401    (Patent Document 3) Unexamined Japanese Patent Application Publication No. 9-309001    (Patent Document 4) Unexamined Japanese Patent Application Publication No. 2002-126901
However, when the vibration body is fixed with a flange-shaped supporting body provided on the outer periphery of the vibration body, especially the restraint against a bending vibration is too strong and problems is caused so that the vibration body cannot provides the specific performance, causes a large vibration energy loss, increases a heating value, and accordingly, it is difficult to employ the structure for a bending vibration. Therefore, a structure for fixing the vibration body by clamping the vibration body with screw-type supporting members in a way that the vibration body is pressed by the pressure surrounding the vibration body is desired.
However, when the vibration body is clamped by screw-shaped supporting members, rigidity for holding the oscillator is lowered, and when conducting high precision processing such as that for an optical surface, a problem of an irregularity pattern is caused on the processed surface by uncontrollable vibration called chatter marks.
Further, when the screw-shaped supporting members supporting the vibration body are loosened, or when a heavy load is applied on the oscillator, there have sometimes been problems where a position for supporting the vibration body is changed and the state of vibration of the vibration body is worsened.
In view of the aforesaid background, an objective of the present invention is to provide an vibration body for cutting operation having an appropriate restraint against bending vibration wherein generation of chatter marks can be controlled and a change in a position of supporting the vibration body can be controlled, a vibration cutting unit and a processing apparatus in which the vibration body for cutting operation is incorporated.
Further objective of the invention is to provide a molding die and an optical element made accurately by using the aforesaid vibration cutting unit.